Hb A₂-Pasteur-Tunis [δ59(E3)Lys→Asn, AAG→AAC]: A New δ Chain Variant Detected by DNA Sequencing in a Tunisian Carrier of the Codon 39 (C→T) β⁰-Thalassemia Mutation

Abstract

We describe a new delta-globin variant, Hb A2-Pasteur-Tunis [delta59(E3)Lys-->Asn, AAG-->AAC]. This hemoglobin (Hb) displayed an electrophoretic mobility faster than normal Hb A2 and was expressed at 2.2 %. The molecular defect was characterized by DNA sequencing and confirmed by a polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP)-designed protocol. Hb A2-Pasteur-Tunis was found in a carrier of a codon 39 (C-->T) beta0-thalassemia (thal), presenting with a normal Hb A2 level. Phenotype and genotype investigations revealed that the total Hb A2 level of the patient was that expected for a minor beta-thal (4.8%).

Rare hemoglobin variants in Tunisian population

“…The δ‐globin variants are not associated with a severe phenotype, but they interfere with the diagnosis of beta‐thalassemia especially in simple carriers. In fact, the presence of such variants leads to the decrease of Hb A 2 levels contrasting with decreased hematological indices, which creates an ambiguity in the diagnosis of an associated beta‐thalassemia . This problem is more important especially when the δ‐globin variant is unstable and at the consequence not detected by phenotyping techniques.…”

“…This mixture could explain this important number and the variability of the rare Hb variants observed in Tunisia. Moreover, rare Hb variants such as Hb Bab‐Saadoun, Hb Kairouan which is associated to a severe β‐thal phenotype, Hb Tunis‐Bizerte (α 1 ‐variant) are originated from Tunisia, and recently, Hb A 2 ‐Pasteur‐Tunis (δ‐variant) was described for the first time (Table ) .…”

“…Genomic DNA was isolated from peripheral blood leukocytes by phenol/chloroform extraction. Polymerase chain reaction (PCR) was used to amplify different fragments corresponding to the coding regions of the concerned genes (α‐, β‐, or δ‐globin), using respective couples of primers . The PCR products were then purified and sequenced automatically by the dye terminator method (ABI PRISM ® 3700 DNA Analyzer; PE Biosystems, Foster City, CA, USA) with the same primers used in the PCR protocol improved, if needed, by additional internal ones.…”

Two new β+‐thalassemia mutation [β ‐56 (G → C); HBBc. −106 G → C] and [β −83 (G → A); HBBc. −133 G → A] described among the Tunisian population

“…1). PCR amplifications were performed as previously described (Chouk et al, 2004;Moumni et al, 2007). The PCR products were treated with exonuclease I and shrimp alkaline phosphatase (New England Biolabs) at 37 C for 30 min followed by heat inactivation at 80 C for 15 min to remove unincorporated nucleotides and excess of primers.…”

Synthetic review on the different anthropological aspects of hemoglobinopathies in Tunisia

“…The assays for antenatal diagnosis for hemoglobinopathies began in 1983 using the association between mutations in the β-globin gene and RFLP haplotypes on the β-globin locus (Beldjord et al, 1983). Today, in Tunisia, the combination of molecular biology techniques, such as ARMS-PCR, RFLP-PCR, DGGE and sequencing, allows prenatal diagnosis in a rapid, reliable and inexpensive way, more particularly in families with an index case (Laradi et al, 2000;Fattoum 2006;Moumni et al, 2007).…”